xifthen – Extended conditional commands

This pack­age ex­tends the ifthen
pack­age by
im­ple­ment­ing new com­mands to go within the first ar­gu­ment of
\ifthenelse: to test whether a string is void or not, if
a com­mand is de­fined or equiv­a­lent to an­other. The pack­age also
en­ables use of com­plex ex­pres­sions as in­tro­duced by the pack­age
calc, to­gether with the abil­ity of
defin­ing new com­mands to han­dle com­plex tests.